1. Field of the Invention
The present invention relates to a recording apparatus and a playback apparatus of image signals, and in particular, to a compression recording apparatus in which obtained image signals are compressed so as to record the compressed data on a recording medium, an expansion playback apparatus in which the compressed data is read from the recording medium so as to be expanded for a playback operation, and a recoding apparatus in which the data of image signals is recorded together with data of voice or audio signals on a recording medium.
2. Description of the Prior Art
In a case where image signals produced by a solid-state imaging apparatus such as a charge-coupled device, CCD are stored in a storage for example, a memory card or a magnetic disk, data of the image signals are required to be compressed, by taking the capacity of the storage into consideration, to a small capacity. As a method of compressing image data, there has been known, for example, a orthogonal transform coding, which will be described below.
First, an image represented by the image signals is subdivided into a predetermined number of blocks so as to conduct a orthogonal transform on data of pixels for each subdivided block.
In the image signals, a low-frequency component thereof occupies a large portion with respect to power, whereas a high-frequency component, although not occupying a great power portion, is considerably significant in a sense of information. In addition, visual characteristics vary between these components. In this situation, the image signals are converted into such low- and high-frequency components so as to respectively undergo suitable quantization, thereby storing coded signals in a storage such as a memory card. On the playback side, the coded signals read from the storage are reversely transformed to attain the original signals.
Incidentally, when considering the storage of image signals on a memory card, it is desirable to use greater compression ratio of the image data. However, a reproducibility of an image or a picture quality is naturally influenced by the image data compression ratio. In consequence, since a high reproducibility is required depending on a purpose of the user, there may appear a disadvantage if the image data compression ratio is increased regardless of various cases. On the other hand, it is economically disadvantageous to prepare a plurality of apparatuses associated with different compression ratios; in consequence, there is desired an apparatus capable of changing the image data compression ratio depending on the requirement, which further leads to a need for a playback apparatus capable of reproducing an image according to the change in the compression ratio in the recording operation.
For the requirement above, there has been proposed an apparatus, for example, in the Japanese Patent Laid-Open No. 61-135286. In this apparatus, after data of pixels undergo a orthogonal transform, a coefficient omission threshold value is set such that a subtraction of this threshold value is conducted on the image data, thereby effecting the compression of the data. Namely, in the subtraction of the threshold value from the image data, the threshold value is varied so as to select a picture quality of the reproduced image. In the case of this apparatus, after the subtraction of the threshold value is effected on the image data, a bit allocation to record data in an external memory such as a memory cartridge, namely, an coding operation is achieved depending on uniform data. In consequence, in a playback apparatus, after data read from the external memory is decoded, it is necessary to add thereto the threshold value employed in the compression of the data; in consequence, data of the threshold value is required to be supplied to the playback apparatus for each playback operation.
On the other hand, it has been known to store still image signals together with audio signals on a storage such as a memory card or a magnetic disk.
In a recording operation on such a storage, for example, it is desirable that voices attained from an object at the respective image shooting operations and data of voices, for example, of an explanation of an obtained image are recorded together with the image data. In such a case, audio data is recorded on a recording medium together with the image data.
Incidentally, since the amount of image data does not vary between respective still images, namely, a fixed amount of image data is produced for each sheet of still picture, a fixed amount of recording area is used in the storage when a picture is recorded. Consequently, the operator need only count the number of stored still pictures, in a case where the storage capacity of the recording medium is known, to obtain the number of pictures to be further stored therein, namely, the remaining storage area of the recording medium.
In contrast thereto, for the audio data, the length of the voices associated with a picture is variable, and hence the amount of the audio data changes between pictures. Consequently, when the audio data are stored in a recording medium together with the image or picture data, the amount of the picture and voice data to be further recorded in the recording medium, namely, the remaining available storage capacity of the recording medium cannot be attained only by counting the number of the pictures already recorded therein. In this situation, it is desired to display the number of pictures as well as the period of voice available for the recording operation, namely, the remaining storage capacity for the pictures as well as for the voice.